Understanding resistance to EGFR inhibitors-impact on future treatment strategies

EGFR expression is linked to osteopontin and Nf-κB signaling in clear cell renal cell carcinoma

AIM AND BACKGROUND

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase involved in many important aspects of cell biology that are related to tumorigenesis. There are opposite evidences of the role of EGFR in renal cancer and the outcome of EGFR-targeted therapies, suggesting the complexity of EGFR signaling pathways. In vitro, osteopontin (OPN) and nuclear factor kappa B (NF-κB) are thought to be involved in specific ligand-independent EGFR activation that could have a role in resistance to EGFR mAb therapy. Aim of this study was to analyze the relationship between EGFR and OPN at the protein and mRNA level, as well as their relation to NF-κB in clear cell renal cell carcinoma (CCRCC).

MATERIALS AND METHODS

Expression of EGFR, OPN, and p65 NF-κB protein was analyzed using immunohistochemistry and compared mutually in 88 CCRCC samples. Expression of EGFR and OPN mRNAs was analyzed using quantitative Real-time PCR in 22 CCRCC samples and compared mutually and with NF-κB protein expression.

RESULTS

Epidermal growth factor receptor mRNA level was higher in CCRCC samples in comparison with normal renal tissue (p = 0.012) and was associated with high OPN mRNA level, and with NF-κB activation (p < 0.001 and p = 0.045, respectively). Immunohistochemical staining showed the inverse association; high EGFR protein expression was related with low OPN and NF-κB protein expression (p < 0.001 and p = 0.047, respectively).

CONCLUSION

Epidermal growth factor receptor gene is upregulated in CRCC and associated with OPN gene expression and NF-kB signaling. The inverse relation between OPN and EGFR at the protein level could probably reflect dynamic changes that EGFR undergoes following activation.

Epidermal growth factor receptor inhibits colitis-associated cancer in mice

Inflammatory bowel disease (IBD) is a chronic illness caused by complex interactions between genetic and environmental factors that propagate inflammation and damage to the gastrointestinal epithelium. This state of chronic inflammation increases the risk for development of colitis-associated cancer in IBD patients. Thus, the development of targeted therapeutics that can disrupt the cycle of inflammation and epithelial injury is highly attractive. However, such biological therapies, including those targeting epidermal growth factor receptor pathways, pose a risk of increasing cancer rates. Using two mouse models of colitis-associated cancer, we found that epidermal growth factor receptor inactivation accelerated the incidence and progression of colorectal tumors. By modulating inflammation and epithelial regeneration, epidermal growth factor receptor optimized the response to chronic inflammation and limited subsequent tumorigenesis. These findings provide important insights into the pathogenesis of colitis-associated cancer and suggest that epidermal growth factor-based therapies for IBD may reduce long-term cancer risk.

YM155 induces EGFR suppression in pancreatic cancer cells

YM155, which inhibits the anti-apoptotic protein survivin, is known to exert anti-tumor effects in various cancers, including prostate and lung cancer. However, there are few reports describing the inhibitory effect of YM155 on human pancreatic cancers that highly express survivin. Here, we tested the effects of YM155 on a variety of cancer cell lines, including pancreatic cancer cells. We found that YM155 exerts an anti-proliferative effect in pancreatic cancer cells, inducing cell death through suppression of XIAP (X-linked inhibitor of apoptosis) as well as survivin without affecting the anti-apoptotic proteins Bcl-xL or Mcl-1. YM155 also inhibited tumor growth in vivo, reducing the size of pancreatic cancer cell line MIAPaCa-2 xenografts by 77.1% on day 31. Western blot analyses further showed that YM155 downregulated phosphoinoside 3-kinase (PI3K) expression and reduced the levels of phosphorylated (activated) extracellular signal-regulated kinase (ERK) and STAT3 (signal transducer and activator of transcription 3) in PANC-1 cells. Interestingly, we also found that YM155 downregulated the epidermal growth factor receptor (EGFR) in various cancer cell lines and induced the EGFR phosphorylation and ubiquitination of EGFR in PANC-1 cells. YM155 also modestly promoted the ubiquitination of survivin and XIAP. Therefore, YM155 acts through modulation of EGFR and survivin expression to subsequently reduce survival. We suggest that YM155 has potential as a therapeutic agent in the treatment of pancreatic cancer.

Cetuximab alleviates neuropathic pain despite tumour progression

The authors present the case of a 68-year-old male patient with metastatic rectal cancer. A pelvic recurrence resulted in neuropathic pain, radiating down his left leg. The pain was resistant to standard treatments. However, after nearly 3 years of debilitating pain, the patient experienced dramatic relief just hours after an infusion of the antiepidermal growth factor receptor antibody cetuximab. The analgesic effect lasted for 10-12 days and was repeated roughly every 12 days for three and a half years. To test for placebo effect, the patient received (unknown to him) 20% of his usual cetuximab dose and experienced no pain relief. The dramatic analgesic effect was documented in clinical notes, medication lists and in numeric rating scales even while his cancer was in radiological progression. Mitogen-activated protein kinase (MAPK)-signalling is believed to be an important driver of neuropathic pain and therefore, the authors hypothesise a direct inhibition of MAPK-signalling by cetuximab in neuronal or glial cells.

STAT1 gene expression is enhanced by nuclear EGFR and HER2 via cooperation with STAT3

Both EGFR and HER2 are important mediators of tumorigenesis and tumor progression. Despite their best-characterized roles as plasma membrane-bound receptors, both receptors undergo nuclear translocation though the impact of this process remains unclear. In this study, we provide evidence showing that EGFR upregulates expression of signal transducer and activator of transcription 1 (STAT1), a transcription factor responding to inflammatory signals and regulating genes involved in inflammatory response. EGFR regulation of STAT1 expression is primarily attributed to the nuclear activity of EGFR. The oncogenic transcription factor STAT3 binds to the STAT1 promoter and synergizes with nuclear EGFR to significantly enhance STAT1 gene expression. Structural characterization of the human STAT1 gene promoter indicates the presence of four functional STAT3-binding sites in the promoter and their importance in STAT1 co-regulation by EGFR and STAT3. The constitutively activated EGFR variant, EGFRvIII, also cooperates with STAT3 to activate the STAT1 gene promoter through the identified STAT3-binding sites within the promoter. Using human breast cancer cell lines, we further found a positive association between levels of STAT1, EGFR, and p-STAT3. Furthermore, we found that STAT1 expression is transcriptionally upregulated by HER2 and heregulin stimulation in breast cancer cells, and the level is further augmented by activated STAT3. In summary, we report in this study that STAT1 expression is upregulated by nuclear EGFR, EGFRvIII and HER2, and that STAT3 synergizes with the three receptors to further enhance STAT1 expression. These novel findings establish a novel link between the mitogenic ErbB signaling pathway and the inflammatory pathway mediated by STAT1.

A targeted enzyme approach to sensitization of tyrosine kinase inhibitor-resistant breast cancer cells

Gefitinib is an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) of potential use in patients with breast cancer. Unfortunately, in clinical studies, gefitinib is often ineffective indicating that resistance to EGFR inhibitors may be a common occurrence in cancer of the breast. EGFR has been shown to be overexpressed in breast cancer, and in particular remains hyperphosphorylated in cell lines such as MDA-MB-468 that are resistant to EGFR inhibitors. Here, we investigate the cause of this sustained phosphorylation and the molecular basis for the ineffectiveness of gefitinib. We show that reactive oxygen species (ROS), known to damage cellular macromolecules and to modulate signaling cascades in a variety of human diseases including cancers, appear to play a critical role in mediating EGFR TKI-resistance. Furthermore, elimination of these ROS through use of a cell-penetrating catalase derivative sensitizes the cells to gefitinib. These results suggest a new approach for the treatment of TKI-resistant breast cancer patients specifically, the targeting of ROS and attendant downstream oxidative stress and their effects on signaling cascades.

Managing drug resistance in cancer: lessons from HIV therapy

Drug resistance is a common cause of treatment failure for HIV infection and cancer. The high mutation rate of HIV leads to genetic heterogeneity among viral populations and provides the seed from which drug-resistant clones emerge in response to therapy. Similarly, most cancers are characterized by extensive genetic, epigenetic, transcriptional and cellular diversity, and drug-resistant cancer cells outgrow their non-resistant peers in a process of somatic evolution. Patient-specific combination of antiviral drugs has emerged as a powerful approach for treating drug-resistant HIV infection, using genotype-based predictions to identify the best matched combination therapy among several hundred possible combinations of HIV drugs. In this Opinion article, we argue that HIV therapy provides a 'blueprint' for designing and validating patient-specific combination therapies in cancer.

Activation of the RAS/RAF/ERK signaling pathway contributes to resistance to sunitinib in thyroid carcinoma cell lines

CONTEXT

Sunitinib is currently being evaluated in advanced human thyroid carcinomas, based on the rationale that the vascular endothelial growth factor and platelet-derived growth factor receptors and the RET/PTC rearrangement are valuable targets for the treatment of this malignancy. However, criteria for selecting thyroid tumors that may benefit from sunitinib are lacking.

DESIGN

The effect of activating somatic mutations in the KRAS and BRAF genes on the responsiveness to sunitinib was evaluated in a panel of thyroid cancer cell lines harboring wild-type KRAS and BRAF genes, the RET/PTC1 rearrangement, the G12R KRAS, or the V600E BRAF mutation.

RESULTS

Sunitinib was found to selectively inhibit cell proliferation, induce cell accumulation in the G0-G1 phase, and inhibit the phosphorylation of ERK1/2 in both KRAS/BRAF wild-type thyroid cancer cells and in tumor cells harboring the RET/PTC rearrangement, whereas it was completely ineffective in KRAS- or BRAF-mutated thyroid carcinoma cells. This differential antitumor activity of sunitinib did not correlate with the expression profile of the vascular endothelial growth factor receptors 1, 2, and 3, platelet-derived growth factor receptor-α and cKIT genes. Of note, the constitutive activation of RAS/RAF/ERK signaling in KRAS/BRAF wild-type cells by transfection of the R12 HRAS or V600E BRAF mutants or stimulation with epithelial growth factor resulted in the loss of responsiveness to sunitinib, whereas pharmacological inhibition of MAPK kinase activity resulted in the resensitization of KRAS- or BRAF-mutated cells to the multikinase inhibitor.

CONCLUSIONS

The constitutive activation of the RAS/RAF/ERK pathway may favor resistance to sunitinib in thyroid carcinoma cells.

The molecular basis for novel therapies

The era of targeted therapy for glioblastoma has arrived, but results have been modest thus far. This review highlights the challenges inherent to treating glioblastoma with targeted therapy and delves into the complex signaling networks that form the molecular basis of novel therapies. Past failures, current challenges, and future possibilities are discussed in the context of the classic "oncogenic" signaling network, as well as the "nononcogenic" stress response network.

Suppression of the epidermal growth factor receptor inhibits epithelial-mesenchymal transition in human pancreatic cancer PANC-1 cells

BACKGROUND

Aberrant expression of epidermal growth factor receptor (EGFR) has been detected in pancreatic cancer; however, the mechanisms of EGFR in inducing pancreatic cancer development have not been adequately elucidated. The objective of this study was to determine the role of EGFR in mediating epithelial-mesenchymal transition (EMT) in pancreatic cancer cells.

METHODS

Pancreatic cancer cell line PANC-1 was transfected with small interfering RNA of EGFR by use of a lentiviral expression vector to establish an EGFR-knockdown cell line (si-PANC-1). PANC-1 cells transfected with lentiviral vector expressing negative control sequence were used as negative control (NC-PANC-1). Scratch assay and transwell study were used to analyze cell migration and invasion. Real-time PCR and Western blotting were used to detect the expression of EMT markers E-cadherin, N-cadherin, vimentin, and fibronectin and transcription factors snail, slug, twist1, and sip1 in PANC-1, NC-PANC-1, and si-PANC-1 cells. Immunofluorescent staining with these antibodies and confocal microscopy were used to observe their cellular location and morphologic changes.

RESULTS

After RNA interference of EGFR, the migration and invasion ability of si-PANC-1 cells decreased significantly. The expression of epithelial phenotype marker E-cadherin increased and the expression of mesenchymal phenotype markers N-cadherin, vimentin, and fibronectin decreased, indicating reversion of EMT. We also observed intracellular translocation of E-cadherin. Expression of transcription factors snail and slug in si-PANC-1 cells decreased significantly.

CONCLUSION

Suppression of EGFR expression can significantly inhibit EMT of pancreatic cancer PANC-1 cells. The mechanism may be related with the down-regulation of the expression of transcription factors snail and slug.

Cetuximab in non-melanoma skin cancer

INTRODUCTION

Non-melanoma skin cancer (NMSC) has become the most common cancer with squamous cell carcinoma (SCC) as the major cause of morbidity and mortality. REVIEW AREAS COVERED: The chimeric human-mouse monoclonal antibody Cetuximab against epidermal growth factor receptor (EGFR) has been approved for advanced head and neck cancer (HNC). Since SCC has been shown to express the EGFR, EGFR-targeted therapy is an option.

METHODOLOGY

A PUBMED research 2000 - 2012 have been conducted using the following items: "Non-melanoma skin cancer AND cetuximab," "cutaneous squamous cell carcinoma AND cetuximab," and "basal cell carcinoma AND cetuximab."

RESULTS

Current evidence of cetuximab efficacy in NMSC results from a Phase II trial and case reports. Cetuximab can be combined with radiotherapy in analogy to HNC. The total response rate is almost 50% in patients with SCC. The combination with radiotherapy resulted in a complete response rate of 50%. Management of adverse reactions in SCC with particular emphasis on cutaneous toxicities is necessary. Further controlled trials are needed.

EXPERT OPINION

EGFR inhibitor cetuximab is an option for recurrent or advanced SCC of skin. The combination with radiotherapy seems to be superior to cetuximab alone.

Constitutive overexpression of the oncogene Rac1 in the airway of recurrent respiratory papillomatosis patients is a targetable host-susceptibility factor

Recurrent respiratory papillomatosis (RRP) is caused by human papillomaviruses (HPVs), primarily types 6 and 11. The disease is characterized by multiple recurrences of airway papillomas, resulting in high levels of morbidity and significant mortality. The prevalence of latent HPV in the larynx of the general population is much greater than the prevalence of RRP, suggesting a host-susceptibility factor for disease. We report that the oncogene Rac1 and its downstream product cyclooxygenase-2 (COX-2) are both constitutively expressed at high levels throughout the airway of these patients, independent of active HPV infection. Use of the COX-2 inhibitor celecoxib in primary papilloma cell culture resulted in the downregulation of HPV transcription. Furthermore, a proof-of-principle study treating three patients with severe RRP with celecoxib resulted in remission of disease in all cases. Therefore, we have identified the first pharmacologically targetable host-susceptibility pathway that contributes to RRP recurrence.

A deuterated analog of dasatinib disrupts cell cycle progression and displays anti-non-small cell lung cancer activity in vitro and in vivo

The pan-Src family kinase inhibitor dasatinib has been approved for chronic myeloid leukemia treatment but displays limited activity in lung cancer patients. In this study, we used a deuterium substitution strategy to develop a class of novel chemicals based on dasatinib and found that these compounds maintain inhibition on c-Src activity and display anti-non-small cell lung cancer activity in vitro and in vivo. BRP800, one of these compounds, was chosen for further studies. BRP800 mainly displayed antiproliferative but not proapoptotic activity. Molecularly, BRP800 did not show significant effects on the expression of antiapoptotic genes, such as Bcl-2 and Mcl1, or on the activation of apoptotic enzymes, such as caspase-3, -8 or 9. However, BRP800 decreased expression of cell cycle promoting genes such as cyclins D1, D3, E, A and CDK4 and 6, and increased the expression of cell cycle negative regulators including p21, p27 and p53. Consistent with these findings, BRP800 arrested cells at the G0/G1 phase in a concentration-dependent manner, and the G0/G1 fraction was increased from 64% in control to 85% in BRP800-treated cells. We also evaluated the effects of BRP800 on NSCLC xenografts using H460 as a model in nude mice. Compared with the known NSCLC drug docetaxel, BRP800 displayed potent and similar antitumor activity but with less toxicity. These findings suggest that the deuterated analog of dasatinib is antiproliferative by inhibiting c-Src and disrupting cell cycle progression, and could be further developed as a novel drug for non-small lung cancer treatment.

TRPC1 protein channel is major regulator of epidermal growth factor receptor signaling

TRP channels have been associated with cell proliferation and aggressiveness in several cancers. In particular, TRPC1 regulates cell proliferation and motility, two processes underlying cancer progression. We and others have described the mechanisms of TRPC1-dependent cell migration. However, the involvement of TRPC1 in cell proliferation remains unexplained. In this study, we show that siRNA-mediated TRPC1 depletion in non small cell lung carcinoma cell lines induced G(0)/G(1) cell cycle arrest resulting in dramatic decrease in cell growth. The expression of cyclins D1 and D3 was reduced after TRPC1 knockdown, pointing out the role of TRPC1 in G(1)/S transition. This was associated with a decreased phosphorylation and activation of EGFR and with a subsequent disruption of PI3K/Akt and MAPK downstream pathways. Stimulation of EGFR by its natural ligand, EGF, induced Ca(2+) release from the endoplasmic reticulum and Ca(2+) entry through TRPC1. Ca(2+) entry through TRPC1 conversely activated EGFR, suggesting that TRPC1 is a component of a Ca(2+)-dependent amplification of EGF-dependent cell proliferation.

Molecular pathology of lung cancer: key to personalized medicine

The majority of lung adenocarcinoma patients with epidermal growth factor receptor- (EGFR) mutated or EML4-ALK rearrangement-positive tumors are sensitive to tyrosine kinase inhibitors. Both primary and acquired resistance in a significant number of those patients to these therapies remains a major clinical problem. The specific molecular mechanisms associated with tyrosine kinase inhibitor resistance are not fully understood. Clinicopathological observations suggest that molecular alterations involving so-called 'driver mutations' could be used as markers that aid in the selection of patients most likely to benefit from targeted therapies. In this review, we summarize recent developments involving the specific molecular mechanisms and markers that have been associated with primary and acquired resistance to EGFR-targeted therapy in lung adenocarcinomas. Understanding these mechanisms may provide new treatment avenues and improve current treatment algorithms.

Cord blood stem cells inhibit epidermal growth factor receptor translocation to mitochondria in glioblastoma

BACKGROUND

Overexpression of EGFR is one of the most frequently diagnosed genetic aberrations of glioblastoma multiforme (GBM). EGFR signaling is involved in diverse cellular functions and is dependent on the type of preferred receptor complexes. EGFR translocation to mitochondria has been reported recently in different cancer types. However, mechanistic aspects of EGFR translocation to mitochondria in GBM have not been evaluated to date.

METHODOLOGY/PRINCIPLE FINDINGS

In the present study, we analyzed the expression of EGFR in GBM-patient derived specimens using immunohistochemistry, reverse-transcription based PCR and Western blotting techniques. In clinical samples, EGFR co-localizes with FAK in mitochondria. We evaluated this previous observation in standard glioma cell lines and in vivo mice xenografts. We further analyzed the effect of human umbilical cord blood stem cells (hUCBSC) on the inhibition of EGFR expression and EGFR signaling in glioma cells and xenografts. Treatment with hUCBSC inhibited the expression of EGFR and its co-localization with FAK in glioma cells. Also, hUCBSC inhibited the co-localization of activated forms of EGFR, FAK and c-Src in mitochondria of glioma cells and xenografts. In addition, hUCBSC also inhibited EGFR signaling proteins in glioma cells both in vitro and in vivo.

CONCLUSIONS/SIGNIFICANCE

We have shown that hUCBSC treatments inhibit phosphorylation of EGFR, FAK and c-Src forms. Our findings associate EGFR expression and its localization to mitochondria with specific biological functions in GBM cells and provide relevant preclinical information that can be used for the development of effective hUCBSC-based therapies.

The cell surface glycoprotein CUB domain-containing protein 1 (CDCP1) contributes to epidermal growth factor receptor-mediated cell migration

Epidermal growth factor (EGF) activation of the EGF receptor (EGFR) is an important mediator of cell migration, and aberrant signaling via this system promotes a number of malignancies including ovarian cancer. We have identified the cell surface glycoprotein CDCP1 as a key regulator of EGF/EGFR-induced cell migration. We show that signaling via EGF/EGFR induces migration of ovarian cancer Caov3 and OVCA420 cells with concomitant up-regulation of CDCP1 mRNA and protein. Consistent with a role in cell migration CDCP1 relocates from cell-cell junctions to punctate structures on filopodia after activation of EGFR. Significantly, disruption of CDCP1 either by silencing or the use of a function blocking antibody efficiently reduces EGF/EGFR-induced cell migration of Caov3 and OVCA420 cells. We also show that up-regulation of CDCP1 is inhibited by pharmacological agents blocking ERK but not Src signaling, indicating that the RAS/RAF/MEK/ERK pathway is required downstream of EGF/EGFR to induce increased expression of CDCP1. Our immunohistochemical analysis of benign, primary, and metastatic serous epithelial ovarian tumors demonstrates that CDCP1 is expressed during progression of this cancer. These data highlight a novel role for CDCP1 in EGF/EGFR-induced cell migration and indicate that targeting of CDCP1 may be a rational approach to inhibit progression of cancers driven by EGFR signaling including those resistant to anti-EGFR drugs because of activating mutations in the RAS/RAF/MEK/ERK pathway.

The regulatory role of the juxtamembrane region in the activity of the epidermal growth factor receptor

Although the EGFR (epidermal growth factor receptor) was discovered over 30 years ago, its mechanism of activation is still the subject of intense study. There are many published studies on the mechanism of EGFR activation and regulation, including biochemical and biophysical analyses and crystallographic structures of EGFR in different activation states and conformations, mutated at various amino acids or bound to different pharmacological inhibitors. The cumulative biochemical, biophysical and structural data have led to a nearly complete account of the mechanism of activation of EGFR. The role of the JXM (juxtamembrane) domain in EGFR structure and activity has only recently begun to be elucidated through biochemical, biophysical and structural studies. In the present article, I review the studies that have highlighted the role of the JXM domain in EGFR activation.

Landscape of EGFR signaling network in human cancers: biology and therapeutic response in relation to receptor subcellular locations

The epidermal growth factor receptor (EGFR) pathway is one of the most dysregulated molecular pathways in human cancers. Despite its well-established importance in tumor growth, progression and drug-resistant phenotype over the past several decades, targeted therapy designed to circumvent EGFR has yielded only modest clinical success in cancer patients, except those with non-small cell lung cancer (NSCLC) carrying EGFR activation mutations. However, almost all of these NSCLC patients eventually developed resistance to small molecule EGFR kinase inhibitors. These disappointing outcomes are, in part, due to the high complexity and the interactive nature of the EGFR signaling network. More recent compelling evidence further indicates that EGFR functionality can be dependent on its subcellular location. In this regard, EGFR undergoes translocation into different organelles where it elicits distinctly different functions than its best known activity as a plasma membrane-bound receptor tyrosine kinase. EGFR can be shuttled into the cell nucleus and mitochondrion upon ligand binding, radiation, EGFR-targeted therapy and other stimuli. Nuclear EGFR behaves as transcriptional regulator, tyrosine kinase, and mediator of other physiological processes. The role of mitochondrial EGFR remains poorly understood but it appears to regulate apoptosis and autophagy. While studies using patient tumors have shown nuclear EGFR to be an indicator for poor clinical outcomes in cancer patients, the impact of mitochondrial EGFR on tumor behavior and patient prognosis remains to be defined. Most recently, several lines of evidence suggest that mislocated EGFR may regulate tumor response to therapy and that plasma membrane-bound EGFR elicits survival signals independent of its kinase activity. In light of these recent progresses and discoveries, we will outline in this minireview an emerging line of research that uncovers and functionally characterizes several novel modes of EGFR signaling that take center stage in the cell nucleus, mitochondrion and other subcellular compartments. We will also discuss the clinical implications of these findings in the rationale design for therapeutic strategy that overcomes tumor drug resistance.

Sialylation of epidermal growth factor receptor regulates receptor activity and chemosensitivity to gefitinib in colon cancer cells

β-Galactoside α2,6-sialyltransferase (ST6Gal-I) has been shown to catalyze α2,6 sialylation of N-glycan, an action that is highly correlated with colon cancer progression and metastasis. We have recently demonstrated that ST6Gal-I-induced α2,6 sialylation is critical for adhesion and migration of colon cancer cells. Increase of α2,6 sialylation also contributes to radioresistance of colon cancer. A number of studies have focused on the involvement of sialylation in tumorigenesis, but the mechanism underlying ST6Gal-I-induced cancer progression and the identity of enzyme substrates has received scant research attention. To provide further support for the relevance of ST6Gal-I in the malignancy of colon cancer, we prepared and characterized a ST6Gal-I-knockdown SW480 colorectal carcinoma cell line. We found that inhibition of ST6Gal-I expression increased cell proliferation and tumor growth in vitro and in vivo. An examination of the effect of sialylation on epidermal growth factor receptor (EGFR) activity and downstream signaling, which are highly correlated with cell proliferation, showed that the loss of ST6Gal-I augmented EGF-induced EGFR phosphorylation and activation of extracellular signal-regulated kinase (ERK) in colon cancer cells. Moreover, ST6Gal-I induced sialylation of both wild type and mutant EGFR. These studies provide the first demonstration that ST6Gal-I induces EGFR sialylation in human colon cancer cell lines. Importantly, the anticancer effect of the EGFR kinase inhibitor, gefitinib, was increased in ST6Gal-I-deficient colon cancer cells. In contrast, overexpression of ST6Gal I decreased the cytotoxic effect of gefitinib. These results suggest that sialylation of the EGFR affects EGF-mediated cell growth and induces chemoresistance to gefitinib in colon cancer cells.

Novel targeted therapies in head and neck cancer

INTRODUCTION

Molecularly targeted therapy, with the potential for increased selectivity and fewer adverse effects, hold promise in the treatment of HNSCC.

AREAS COVERED

Targeted agents for HNSCC expected to improve the effectiveness of current therapy including HER family, Src-family kinase, cell cycle, MET, AKT, HDAC, PARP, COX inhibitors and antiangiogenesis.

EXPERT OPINION

Epidermal growth factor receptor inhibitors are established in HNSCC and the need now is to find biomarkers for sensitivity to better select patients. Moreover, other pathway inhibitors hold significant promise and are being tested in clinical trials. Angiogenesis inhibition is likely to yield only modest efficacy alone but may augment existing standards. Lastly, one clinical arena where targeted therapies may find secure purchase is in the adjuvant or prevention setting where minimal or preneoplastic disease can be affected by inhibition of a single or few targets.

Proteomic analysis identifies differentially expressed proteins after HDAC vorinostat and EGFR inhibitor gefitinib treatments in Hep-2 cancer cells

Several solid tumors are characterized by poor prognosis and few effective treatment options, other than palliative chemotherapy in the recurrent/metastatic setting. Epidermal growth factor receptor (EGFR) has been considered an important anticancer target because it is involved in the development and progression of several solid tumors; however, only a subset of patients show a clinically meaningful response to EGFR inhibition, particularly to EGFR tyrosine kinase inhibitors such as gefitinib. We have recently demonstrated synergistic antitumor effect of the histone deacetylase inhibitor vorinostat combined with gefitinib. To further characterize the interaction between these two agents, cellular extracts from Hep-2 cancer cells that were untreated or treated for 24 h with either vorinostat or gefitinib alone or with a vorinostat/gefitinib combination were analyzed using 2-D DIGE. Software analysis using DeCyder was performed, and numerous differentially expressed protein spots were visualized between the four examined settings. Using MALDI-TOF MS and ESI-Ion trap MS/MS, several differentially expressed proteins were identified; some of these were validated by Western blotting. Finally, a pathway analysis of experimental data performed using MetaCore highlighted a relevant relationship between the identified proteins and additional potential effectors. In conclusion, we performed a comprehensive analysis of proteins regulated by vorinostat and gefitinib, alone and in combination, providing a useful insight into their mechanisms of action as well as their synergistic interaction.

Identification of new peptide ligands for epidermal growth factor receptor using phage display and computationally modeling their mode of binding

Peptide phage display, a powerful method for ligand identification, was used to identify new peptide ligands for epidermal growth factor receptor. A-431 cells expressing epidermal growth factor receptor were used as the matrix in a cell-based subtractive biopanning approach using a 7-mer peptide displaying phage library. Two novel peptide ligands were identified and tested for their affinities and functional effects on epidermal growth factor receptor. The identified peptides were able to inhibit the epidermal growth factor-induced phosphorylation of epidermal growth factor receptor in a concentration-dependent manner. The results of affinity binding experiments showed that the natural ligand, that is epidermal growth factor, was able to inhibit competitively the binding of peptide-bearing phage to epidermal growth factor receptor expressing A-431 cells. Molecular modeling studies were used to calculate the free energies for the binding of peptides to the receptor-binding site as well as proposing the interaction modes for this binding. The calculated values for the binding energies were found to be similar to our experimental data and those of previously reported studies.

Tumor-targeted Nanobullets: Anti-EGFR nanobody-liposomes loaded with anti-IGF-1R kinase inhibitor for cancer treatment

The epidermal growth factor receptor (EGFR) is a validated target for anti-cancer therapy and several EGFR inhibitors are used in the clinic. Over the years, an increasing number of studies have reported on the crosstalk between EGFR and other receptors that can contribute to accelerated cancer development or even acquisition of resistance to anti-EGFR therapies. Combined targeting of EGFR and insulin-like growth factor 1 receptor (IGF-1R) is a rational strategy to potentiate anti-cancer treatment and possibly retard resistance development. In the present study, we have pursued this by encapsulating the kinase inhibitor AG538 in anti-EGFR nanobody-liposomes. The thus developed dual-active nanobody-liposomes associated with EGFR-(over)expressing cells in an EGFR-specific manner and blocked both EGFR and IGF-1R activation, due to the presence of the EGFR-blocking nanobody EGa1 and the anti-IGF-1R kinase inhibitor AG538 respectively. AG538-loaded nanobody-liposomes induced a strong inhibition of tumor cell proliferation even upon short-term exposure followed by a drug-free wash-out period. Therefore, AG538-loaded nanobody-liposomes are a promising anti-cancer formulation due to efficient intracellular delivery of AG538 in combination with antagonistic and downregulating properties of the EGa1 nanobody-liposomes.

Advances in the design and synthesis of prazosin derivatives over the last ten years

INTRODUCTION

Mechanistic, translational and pharmacological studies led to the identification and discovery of the preferred localization, binding characteristics, structure and functional properties of α1-adrenoceptor (α1-AR) subtypes in the bladder neck, bladder and prostate gland. The evidence gathered on α1-ARs, provided a molecular platform for the development of subtype-selective antagonists, resulting in more effective approaches targeting those receptors for the treatment of outlet bladder obstruction and benign prostate hyperplasia.

AREAS COVERED

Advances over the last decade in the design and optimization of Prazosin, Doxazosin and Terazosin quinazoline-based derivatives as α1-AR antagonists. Evidence on the metabolic and growth interference action by these agents, in addition to their smooth-muscle-relaxing effects. The new action recognition emerges from data on the inhibitory effect of quinazoline-based antagonists on primary tumor growth and progression to metastasis. In addition to the cellular findings in the prostate, functional validation and therapeutic effects of selected lead pharmaceutically optimized derivatives in the context of impairing vascularity and triggering tumor apoptosis.

EXPERT OPINION

Knowledge on targeting intracellular signalling pathways driving the cellular response via an α1-AR-dependent and independent antagonistic action, must be invested towards the optimization of new agents that while bypassing AR, exhibit improved pharmacological efficacy against human cancer.

Overcoming molecular mechanisms of resistance to first-generation epidermal growth factor receptor tyrosine kinase inhibitors

The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) gefitinib and erlotinib have provided substantial benefits to patients with advanced non-small cell lung cancer (NSCLC). However resistance to these agents has emerged as a significant clinical issue; most patients who initially respond to treatment eventually experience relapse. The mechanisms underlying gefitinib and erlotinib resistance are multifactorial and several have been described. Clearly there is a need for novel and more effective therapies that can overcome resistance to the currently available TKIs. Several agents are in clinical development, including irreversible EGFR TKIs, inhibitors of the MET pathway, and others. In this review we discuss the various underlying mechanisms of gefitinib and erlotinib resistance and highlight the agents currently in clinical development that may have potential for overcoming this resistance.

Protein-intrinsic and signaling network-based sources of resistance to EGFR- and ErbB family-targeted therapies in head and neck cancer

Agents targeting EGFR and related ErbB family proteins are valuable therapies for the treatment of many cancers. For some tumor types, including squamous cell carcinomas of the head and neck (SCCHN), antibodies targeting EGFR were the first protein-directed agents to show clinical benefit, and remain a standard component of clinical strategies for management of the disease. Nevertheless, many patients display either intrinsic or acquired resistance to these drugs; hence, major research goals are to better understand the underlying causes of resistance, and to develop new therapeutic strategies that boost the impact of EGFR/ErbB inhibitors. In this review, we first summarize current standard use of EGFR inhibitors in the context of SCCHN, and described new agents targeting EGFR currently moving through pre-clinical and clinical development. We then discuss how changes in other transmembrane receptors, including IGF1R, c-Met, and TGF-β, can confer resistance to EGFR-targeted inhibitors, and discuss new agents targeting these proteins. Moving downstream, we discuss critical EGFR-dependent effectors, including PLC-γ; PI3K and PTEN; SHC, GRB2, and RAS and the STAT proteins, as factors in resistance to EGFR-directed inhibitors and as alternative targets of therapeutic inhibition. We summarize alternative sources of resistance among cellular changes that target EGFR itself, through regulation of ligand availability, post-translational modification of EGFR, availability of EGFR partners for hetero-dimerization and control of EGFR intracellular trafficking for recycling versus degradation. Finally, we discuss new strategies to identify effective therapeutic combinations involving EGFR-targeted inhibitors, in the context of new system level data becoming available for analysis of individual tumors.

Erlotinib inhibits progression to dysplasia in a colitis-associated colon cancer model

AIM: To investigate the role of epidermal growth factor receptor (EGFR) in colitis-associated dysplasia using the EGFR tyrosine kinase inhibitor erlotinib.

METHODS: Sprague-Dawley rats received trinitrobenzene sulfonic acid (TNBS; 30 mg in 50% ethanol, ic), followed 6 wk later by reactivation with TNBS (5 mg/kg, iv) for 3 d. To induce colitis-associated dysplasia, rats then received TNBS (iv) twice a week for 10 wk. One group received erlotinib (10 mg/kg, ip) for 1 wk before the start of the reactivation of the colitis and 2 wk after (21 d); the rest received the vehicle. After rats were euthanized, the colons were removed and analyzed for damage and expression of the EGFR downstream effectors Erk1/2 and c-Myc.

RESULTS: Ninety percent of the vehicle-treated animals had dysplasia in any region of the colon. Erlotinib-treated animals had a significant decrease in the incidence of dysplasia compared to vehicle-treated animals in all regions of the colon (50.00% ± 11.47% vs 90.00% ± 10.00% in proximal, P < 0.05; 15.00% ± 8.19% vs 50.00% ± 16.67% in mid, P < 0.05; and 20.00% ± 9.17% vs 70.00% ± 15.28% in distal, P < 0.01). Erlotinib-treated animals also had reduced cell proliferation, reduced active Erk1/2, and reduced c-Myc in colon epithelium compared with the vehicle-treated animals. In vitro, erlotinib treatment was shown to markedly decrease c-Myc and pErk1/2 levels in rat epithelial cells. Proliferation of rat epithelial cells was stimulated by epidermal growth factor and inhibited by erlotinib (P < 0.05).

CONCLUSION: Erlotinib can decrease the development of colitis-associated dysplasia, suggesting a potential therapeutic use for erlotinib in patients with long-standing colitis.

Mechanistic insights into the activation of oncogenic forms of EGF receptor

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly activated by mutation in non-small cell lung cancer. The mechanism of this oncogenic activation is not completely understood, but in contrast to that of the wild-type EGFR, it is proposed to be independent of kinase domain dimerization. Mechanistic studies on EGFR have mainly relied on cell-based assays or isolated kinase domain measurements. Here we show, using purified, near full-length human EGFR proteins (tEGFRs), that two oncogenic mutants are fully active independently of EGF and highly resistant to the therapeutic and endogenous inhibitors cetuximab, lapatinib and MIG6. Based on the pattern of inhibition and the effects of additional asymmetric kinase dimer interface mutations, we propose that these oncogenic EGFR mutants drive and strongly depend on the formation of the asymmetric kinase dimer for activation, which has implications for drug design and cancer treatment strategies.

p53 modulates acquired resistance to EGFR inhibitors and radiation

There is presently great interest in mechanisms of acquired resistance to epidermal growth factor receptor (EGFR) inhibitors that are now being used widely in the treatment of a variety of common human cancers. To investigate these mechanisms, we established EGFR inhibitor-resistant clones from non-small cell lung cancer cells. A comparative analysis revealed that acquired resistance to EGFR inhibitors was associated consistently with the loss of p53 and cross-resistance to radiation. To examine the role of p53, we first knocked down p53 in sensitive parental cells and found a reduction in sensitivity to both EGFR inhibitors and radiation. Conversely, restoration of functional p53 in EGFR inhibitor-resistant cells was sufficient to resensitize them to EGFR inhibitors or radiation in vitro and in vivo. Further studies indicate that p53 may enhance sensitivity to EGFR inhibitors and radiation via induction of cell-cycle arrest, apoptosis, and DNA damage repair. Taken together, these findings suggest a central role of p53 in the development of acquired resistance to EGFR inhibitors and prompt consideration to apply p53 restoration strategies in future clinical trials that combine EGFR inhibitors and radiation.

New facets of matrix metalloproteinases MMP-2 and MMP-9 as cell surface transducers: outside-in signaling and relationship to tumor progression

This review focuses on matrix metalloproteinases (MMPs)-2 (gelatinase A) and -9 (gelatinase B), both of which are cancer-associated, secreted, zinc-dependent endopeptidases. Gelatinases cleave many different targets (extracellular matrix, cytokines, growth factors, chemokines and cytokine/growth factor receptors) that in turn regulate key signaling pathways in cell growth, migration, invasion, inflammation and angiogenesis. Interactions with cell surface integral membrane proteins (CD44, αVβ/αβ1/αβ2 integrins and Ku protein) can occur through the gelatinases' active site or hemopexin-like C-terminal domain. This review evaluates the recent literature on the non-enzymatic, signal transduction roles of surface-bound gelatinases and their subsequent effects on cell survival, migration and angiogenesis. Gelatinases have long been drug targets. The current status of gelatinase inhibitors as anticancer agents and their failure in the clinic is discussed in light of these new data on the gelatinases' roles as cell surface transducers - data that may lead to the design and development of novel, gelatinase-targeting inhibitors.

Epithelial junction opener JO-1 improves monoclonal antibody therapy of cancer

The efficacy of monoclonal antibodies (mAb) used to treat solid tumors is limited by intercellular junctions which tightly link epithelial tumor cells to each another. In this study, we define a small, recombinant adenovirus serotype 3-derived protein, termed junction opener 1 (JO-1), which binds to the epithelial junction protein desmoglein 2 (DSG2). In mouse xenograft models employing Her2/neu- and EGFR-positive human cancer cell lines, JO-1 mediated cleavage of DSG2 dimers and activated intracellular signaling pathways which reduced E-cadherin expression in tight junctions. Notably, JO-1-triggered changes allowed for increased intratumoral penetration of the anti-Her2/neu mAb trastuzumab (Herceptin) and improved access to its target receptor, Her2/neu, which is partly trapped in tight junctions. This effect translated directly into increased therapeutic efficacy of trastuzumab in mouse xenograft models using breast, gastric, and ovarian cancer cells that were Her2/neu-positive. Furthermore, combining JO-1 with the EGFR-targeting mAb cetuximab (Erbitux) greatly improved therapeutic outcomes in a metastatic model of EGFR-positive lung cancer. A combination of JO-1 with an approach that triggered transient degradation of tumor stroma proteins elicited eradication of tumors. Taken together, our findings offer preclinical proof of concept to employ JO-1 in combination with mAb therapy.

The landscape of EGFR pathways and personalized management of non-small-cell lung cancer

Two classes of anti-EGF receptor (EGFR) agents, monoclonal anti-EGFR antibodies and small-molecule EGFR tyrosine kinase inhibitors, have been used for the treatment of non-small-cell lung cancer (NSCLC). However, only a subset of patients will benefit from EGFR-targeted therapy. The discovery of biomarkers that select the appropriate patients for the therapy and predict the responses to the therapy is urgently needed. Molecular genetic analyses provide new insights into EGFR pathway alterations and demonstrate promise for predicting the clinical outcome of patients with NSCLC. In this article, we summarize the latest available knowledge on the clinical impact of EGFR mutations, gene copy number, EGFR overexpression, phosphorylation expression and the alteration of the EGFR pathway downstream factors in predicting the response to EGFR-targeted therapy in NSCLC patients. The role of KRAS and BRAF mutations and ALK rearrangement in lung cancer-targeted therapy, are also reviewed.

Cell signaling molecules as drug targets in lung cancer: an overview

PURPOSE OF REVIEW

Lung being one of the vital and essential organs in the body, lung cancer is a major cause of mortality in the modern human society. Lung cancer can be broadly subdivided into nonsmall cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Although NSCLC is sometimes treated with surgery, the advanced and metastatic NSCLC and SCLC usually respond better to chemotherapy and radiation. The most important targets of these chemotherapeutic agents are various intracellular signaling molecules. The primary focus of this review article is to summarize the description of various cell signaling molecules involved in lung cancer development and their regulation by chemotherapeutic agents.

RECENT FINDINGS

Extensive research work in recent years has identified several cellular signaling molecules that may be intricately involved in the complexity of lung cancer. Some of these cell signaling molecules are epidermal growth factor receptors, vascular endothelial growth factor receptors, mammalian target of rapamycin, mitogen-activated protein kinase phosphatase-1, peroxisome proliferator-activated receptor-gamma, matrix metalloproteinases and receptor for advanced glycation end-products.

SUMMARY

The present review will strengthen our current knowledge regarding the efficacy of the above-mentioned cell signaling molecules as potential beneficial drug targets against lung cancer.

Allosteric modulation by protein kinase Cε leads to modified responses of EGF receptor towards tyrosine kinase inhibitors

Recently, we described a novel function of over-expressed protein kinase Cε (PKCε) as a negative allosteric modulator of EGFR signalling in several head and neck squamous carcinoma (HNSCC) cell lines. Extending this work, here we present several lines of evidence for the potency of PKCε to differently modulate the efficacy of EGFR tyrosine kinase inhibitors (TKIs) such as gefitinib and lapatinib. Using the HNSCC cell line FaDu as a model, we demonstrate by co-immunoprecipitation the physical association of over-expressed PKCε with the EGFR which is stabilised by gefitinib and leads to an increase in gefitinib-induced inhibition of EGFR downstream signalling and elevated EGFR-ErbB2 heterodimerisation. Cell cycle and Western blot analysis revealed that the gefitinib-induced apoptosis was enhanced whereas the pro-apoptotic effect of lapatinib that requires another EGFR conformation was reduced by PKCε. Our findings suggest that due to elevated expression PKCε may associate with the EGFR resulting in conformational changes and different allosteric modulation of the EGFR behaviour towards TKIs. This surprising capacity indicates PKCε as a novel predictive marker protein in molecular cancer therapy with EGFR tyrosine kinase inhibitors.

An LXR agonist promotes glioblastoma cell death through inhibition of an EGFR/AKT/SREBP-1/LDLR-dependent pathway

Glioblastoma (GBM) is the most common malignant primary brain tumor of adults and one of the most lethal of all cancers. Epidermal growth factor receptor (EGFR) mutations (EGFRvIII) and phosphoinositide 3-kinase (PI3K) hyperactivation are common in GBM, promoting tumor growth and survival, including through sterol regulatory element-binding protein 1 (SREBP-1)-dependent lipogenesis. The role of cholesterol metabolism in GBM pathogenesis, its association with EGFR/PI3K signaling, and its potential therapeutic targetability are unknown. In our investigation, studies of GBM cell lines, xenograft models, and GBM clinical samples, including those from patients treated with the EGFR tyrosine kinase inhibitor lapatinib, uncovered an EGFRvIII-activated, PI3K/SREBP-1-dependent tumor survival pathway through the low-density lipoprotein receptor (LDLR). Targeting LDLR with the liver X receptor (LXR) agonist GW3965 caused inducible degrader of LDLR (IDOL)-mediated LDLR degradation and increased expression of the ABCA1 cholesterol efflux transporter, potently promoting tumor cell death in an in vivo GBM model. These results show that EGFRvIII can promote tumor survival through PI3K/SREBP-1-dependent upregulation of LDLR and suggest a role for LXR agonists in the treatment of GBM patients.

HDAC inhibitor vorinostat enhances the antitumor effect of gefitinib in squamous cell carcinoma of head and neck by modulating ErbB receptor expression and reverting EMT

Potentiation of epidermal growth factor receptor (EGFR) inhibitors is required in squamous cell carcinoma of head and neck (SCCHN) to improve their therapeutic index. We demonstrated that the histone deacetylase inhibitor vorinostat in combination with the EGFR tyrosine kinase inhibitor gefitinib induced synergistic inhibition of proliferation, migration, and invasion as well as induction of apoptosis in SCCHN cells, including cells resistant to gefitinib. We provided evidence suggesting that differential modulation of ErbB receptors together with reversion of epithelial-to-mesenchymal transition (EMT) by vorinostat represent mechanistic bases for the observed synergism. We demonstrated in epithelial CAL27 cells expressing EGFR, ErbB2, and ErbB3 that vorinostat downregulated the expression and signaling of all three receptors. In gefitinib-resistant KB and Hep-2 cells, both of which had undergone EMT and expressed very low levels of ErbB3, vorinostat reverted the mesenchymal phenotype by inducing both E-cadherin and ErbB3 and downregulating vimentin as well as EGFR and ErbB2. Both transcriptional and post-translational mechanisms were involved in the modulation of ErbB receptors by vorinostat. Attenuation of all ErbB transcripts in CAL27 cells as well as induction of ErbB3 transcript in Hep-2 and KB cells was seen upon vorinostat treatment. We showed that vorinostat induced ubiquitination of EGFR and ErbB2 and targeted them predominantly to lysosome-degradation in all cell lines, while the induction of ErbB3-ubiquitination in CAL27 cells led to proteasomes-degradation. Overall, this study suggests that the vorinostat/gefitinib combination represents a promising therapeutic strategy that warrants further clinical evaluation in SCCHN, including tumors intrinsically resistant to EGFR-inhibitors.

Stem cell property epithelial-to-mesenchymal transition is a core transcriptional network for predicting cetuximab (Erbitux™) efficacy in KRAS wild-type tumor cells

Beyond a well-recognized effect of KRAS mutations in determining de novo inefficacy of cetuximab (CTX) in metastatic colorectal cancer, we urgently need a biomarker signature for predicting CTX efficacy in KRAS wild-type (WT) tumors. CTX-adapted EGFR gene-amplified KRAS WT tumor cell populations were induced by stepwise-chronic exposure of A431 epidermoid cancer cells to CTX. Genome-wide analyses of 44K Agilent's whole human arrays were bioinformatically evaluated by Gene Set Enrichment Analysis (GSEA)-based screening of the KEGG pathway database. Molecular functioning of CTX was found to depend on: (i) The occurrence of a positive feedback loop on Epidermal Growth Factor Receptor (EGFR) activation driven by genes coding for EGFR ligands (e.g., amphiregulin); (ii) the lack of a negative feedback on mitogen-activated protein kinase (MAPK) activation regulated by dual-specificity phosphatases (e.g., DUSP6) and; (iii) the transcriptional status of gene pathways controlling the epithelial-to-mesenchymal transition (EMT) and its reversal (MET) program (actin cytoskeleton and cell-cell communication-e.g., keratins-focal adhesion signaling-e.g., integrins-and EMT-inducing cytokines - e.g., transforming growth factor-β). Quantitative real-time PCR, high-content immunostaining, and flow-cytometry analyses confirmed that CTX efficacy depends on its ability to promote: (i) Stronger cell-cell contacts by up-regulating the expression of the epithelial markers E-cadherin and occludin; (ii) down-regulation of the epithelial transcriptional repressors Zeb, Snail, and Slug accompanied by restoration of cortical F-actin; and (iii) complete prevention of the CD44(pos)/CD24(neg/low) mesenchymal immunophenotype. The impact of EGFR ligands/MAPK phosphatases gene transcripts in predicting CTX efficacy in KRAS WT tumors may be tightly linked with the ability of CTX to concurrently reverse the EMT status, a pivotal property of migrating cancer stem cells.

Membranous expression of ectodomain isoforms of the epidermal growth factor receptor predicts outcome after chemoradiotherapy of lymph node-negative cervical cancer

PURPOSE

We compared the prognostic significance of ectodomain isoforms of the epidermal growth factor receptor (EGFR), which lack the tyrosine kinase (TK) domain, with that of the full-length receptor and its autophosphorylation status in cervical cancers treated with conventional chemoradiotherapy.

EXPERIMENTAL DESIGN

Expression of EGFR isoforms was assessed by immunohistochemistry in a prospectively collected cohort of 178 patients with squamous cell cervical carcinoma, and their detection was confirmed with Western blotting and reverse transcriptase PCR. A proximity ligation immunohistochemistry assay was used to assess EGFR-specific autophosphorylation. Pathways associated with the expression of ectodomain isoforms were studied by gene expression analysis with Illumina beadarrays in 110 patients and validated in an independent cohort of 41 patients.

RESULTS

Membranous expression of ectodomain isoforms alone, without the coexpression of the full-length receptor, showed correlations to poor clinical outcome that were highly significant for lymph node-negative patients (locoregional control, P = 0.0002; progression-free survival, P < 0.0001; disease-specific survival, P = 0.005 in the log-rank test) and independent of clinical variables. The ectodomain isoforms were primarily 60-kD products of alternative EGFR transcripts. Their membranous expression correlated with transcriptional regulation of oncogenic pathways including activation of MYC and MAX, which was significantly associated with poor outcome. This aggressive phenotype of ectodomain EGFR expressing tumors was confirmed in the independent cohort. Neither total nor full-length EGFR protein level, or autophosphorylation status, showed prognostic significance.

CONCLUSION

Membranous expression of ectodomain EGFR isoforms, and not TK activation, predicts poor outcome after chemoradiotherapy for patients with lymph node-negative cervical cancer.